Poly(phenylene ether ether ketone) is one of high-performance super engineering plastics and has excellent heat resistance, excellent chemical resistance and excellent flame retardancy and additionally excellent mechanical properties, such as wear resistance and friction resistance. Because of these excellent properties of poly(phenylene ether ether ketone), the demand for poly(phenylene ether ether ketone) has been expanded, as an alternative of the existing super engineering plastics or as an alternative of the existing metals, extensively in the field of automobile applications, electric and electronic applications and industrial applications.
A generally known industrial production method of this poly(phenylene ether ether ketone) is a method of polymerizing 4,4′-difluorobenzophenone and hydroquinone in diphenyl sulfone by the nucleophilic substitution reaction in the presence of a base (see, for example, Patent Document 1). This production method, however, requires an extremely high temperature of not lower than 300° C. for the reaction in its polymerization process and accordingly has a large energy cost for production. Additionally, this production method needs the use of an expensive solvent having a high boiling point, such as diphenyl sulfone. Moreover, its polymer recovery process requires a multi-stage process and a large amount of an organic solvent (for example, acetone or methanol) to wash the resulting poly(phenylene ether ether ketone) repeatedly, for example, about 10 times with the organic solvent for removal of diphenyl sulfone and subsequently wash the poly(phenylene ether ether ketone) with water for further purification. The conventional production technique of poly(phenylene ether ether ketone) accordingly has problems of extremely high production cost and high environment load.
Cyclic poly(phenylene ether ether ketone) having a poly(phenylene ether ether ketone) skeleton has recently drawn attention as the raw material used for synthesis of a high-molecular weight linear polymer by ring-opening polymerization.
The cyclic poly(phenylene ether ether ketone)s reported previously are, however, only those having the melting point of greater than 270° C.: for example, cyclic poly(phenylene ether ether ketone) having a repeating number m equal to 3 and/or 6 in General Formula (I) given below and having a melting point of 275° C. and cyclic poly(phenylene ether ether ketone) having a repeating number m equal to 4 and having a melting point of 333° C. (Non-Patent Document 1).

The synthesis of poly(phenylene ether ether ketone) by ring-opening polymerization of such cyclic poly(phenylene ether ether ketone) has also been reported. This synthesis is, however, performed in only a temperature range of not lower than 340° C., in other words, in a temperature range of not lower than the melting point of the conventionally known cyclic poly(phenylene ether ether ketone). There has been no description with respect to ring-opening polymerization at the temperature of not higher than the melting point of poly(phenylene ether ether ketone). This may be attributed to that the cyclic poly(phenylene ether ether ketone) used has a high melting point. This method is, however, not advantageous in energy cost, compared with the conventional production method of poly(phenylene ether ether ketone) that does not use the cyclic poly(phenylene ether ether ketone). In the process of ring-opening polymerization of the cyclic poly(phenylene ether ether ketone), the polymerization temperature may become even higher according to the composition of the raw materials used and the type and the amount of an additive added to the raw materials.